The growing evolution of obesity has not spared children and adolescents with intellectual disabilities. Ours studies based on "research-action", with the aim of improving care for people with mental disabilities. Conducted in 5 specialized schools, our first study shows that over 40% of adolescents with intellectual disabilities have an excess body fat. More than 30% of adolescents report a low physical activity level, and only half reaches enough physical activity to avoid an excess of body fat. Moreover, the most active adolescents are less likely to develop an excess body fat. Their low level of physical fitness is a high risk factor to health. For these adolescent with intellectual disabilities, this is an "extra-handicap" which may increase the restriction of social participation and impair quality of life. Being active daily would reduce the health risks, including limiting the obesity development. Thus, we proposed an Adapted Physical Activity program to over-fatness adolescents. This program has helped to increase level of physical activity and stabilize weight, while decreasing fat mass and waist circumference. The interdisciplinary approach of this research has allowed us to consider the evolution of self-concept and to note that it was not altered by this weight management program.